Paragraph One: TOKYO - A powerful earthquake shook northern Japan early Tuesday, and small tsunami waves struck coastal towns about 200 miles from the epicenter. There were no immediate reports of damage or injuries.

Paragraph Two: The quake, with a preliminary magnitude of 7.1, hit at 6:39 a.m. (4:39 p.m. Monday EST) and was centered just below the ocean bottom off the east coast of Japan's main island of Honshu, Japan's Meteorological Agency said.

Paragraph Three: Small tsunami waves measuring 12 and 20 inches hit the coastal city of Ofunato and smaller waves hit at least four other towns. Tsunami waves — generated by earthquakes — are often barely noticeable in the ocean but can rise to great heights once they arrive at shore. Ross Stein, a geophysicist with the USGS in Menlo Park, Calif., said the swell amounted to "a surfable tsunami."

Paragraph Four: The quake hit at a depth of about 18 miles and was centered off the coast of Sanriku in northern Japan, 330 miles east of Tokyo, the U.S. Geological Survey said. It shook buildings across a wide area across northern and eastern Honshu, including Tokyo, and Hokkaido.

Paragraph Five: Japan is one of the world's most earthquake-prone countries because it sits atop four tectonic plates. A 7.2-magnitude earthquake shook northeastern Japan in August, injuring at least 59 people, triggering landslides, damaging buildings and causing widespread power outages.

Concluding Paragraph : There was no destructive Pacific Ocean- wide tsunami threat following Tuesday's earthquake, based on historical quake and tsunami data, according to the Pacific Tsunami Warning Center in Ewa Beach, Hawaii.

However, earthquakes as large as Tuesday's can generate a local tsunami capable of causing destruction along coastlines within 60 miles of the epicenter, according to the center.